Radiation imaging apparatus

ABSTRACT

A single flat panel detector provides radiation images which can correspond with various radiographic modes. In a radiation imaging apparatus including a flat panel detector which derives a radiation image according to incident radiation, a holding unit which holds the flat panel detector and a connecting mechanism capable of performing a connecting and a disconnecting between the holding unit and the flat panel detector, the flat panel detector can be controlled so that the maximum number of radiation images that the flat panel detector can derive when the flat panel detector is disengaged from the holding unit is smaller than the maximum number of radiation images that the flat panel detector can derive when the flat panel detector is held by the holding unit.

RELATED APPLICATIONS

This application is a divisional of patent application Ser. No.11/814,749, filed Jul. 25, 2007, which is the U.S. national phaseapplication of international patent application PCT/JP2007/051535, filedJan. 24, 2007, claims benefit of the filing date of that applicationunder 35 U.S.C. §120, and claims priority benefit under 35 U.S.C. §119of Japanese patent applications nos. 2006-020975 and 2007-004676, filedJan. 30, 2006, and Jan. 12, 2007, respectively. The entire contents ofeach of the mentioned prior domestic and foreign applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION Technical Field of the Invention

The present invention relates to a radiation imaging apparatus suitedfor use in medical diagnosis, for example, and in particular, to aradiation imaging apparatus including a flat panel detector using asemiconductor element as a detector. In the present invention, the term“radiation” includes not only α rays, β rays and γ rays which are beamsof particles (including photons) emitted by radioactive decay, but alsobeams having energy higher than or comparable to that of those rays, forexample, X-rays, particle beams, cosmic rays and others.

DESCRIPTION OF RELATED ART Background Art

Hitherto, an image intensifier (hereinafter, abbreviated to I.I.) hasbeen used as a detector for capturing radiation images in a radiationimaging apparatus for medical diagnosis for use in fluoroscopicradiography. The radiation imaging apparatus using I.I. performsfluoroscopic radiography in such a manner that radiation imageinformation based on radiation that has passed through an object isconverted into optical information and then the optical information isintensified in luminance, condensed and picked up by a camera.

With advances in thin-film semiconductor technology of late, a flatpanel detector described in European Patent Publication No. 0791964 hasbeen practically used as a detector for capturing radiation images. Theflat panel detector has a converting unit in which a plurality of pixelsconsisting of thin film semiconductors are arrayed on an insulatingsubstrate made of glass, and the converting unit converts radiationimage information into an electrical signal to provide imageinformation. The pixel has a converting element which converts radiationinto an electric charge and a switching element which transfers theconverted electric charge. Known converting elements include two types:an indirect-converting type composed of a scintillator which convertsradiation into light and a photoelectric transducer which converts theconverted light into an electric charge; and a direct-converting typeusing a semiconductor material which directly converts radiation into anelectric charge. Known switching elements include: a thin filmtransistor (hereinafter, abbreviated to TFT) composed of a thin filmsemiconductor; and an element using a thin film diode or the like. Theuse of a non-single crystalline semiconductor such as an amorphoussemiconductor or a polycrystalline semiconductor in the pixel composedof the thin film semiconductor enables realizing a detector which islarger in radiographic area and lighter in weight than that using aconventional I.I. FIG. 7 shows an example of the equivalent circuit forthe flat panel detector.

Such a flat panel detector has been used as a detector for capturingstill images such as X-raying using film until now. At present, use of aflat panel detector as a detector for radiographing moving images suchas fluoroscopic radiography and the like has come to be a matter ofinterest and study. Japanese Patent Application Laid-Open No. H11-009579discloses a radiation imaging apparatus using a flat panel detector as adetector. The radiation imaging apparatus uses a flat panel detectorwhich is lighter in weight than and superior in portability to theconventional detector using an I.I. as a detector, so that the flatpanel detector is detachably mounted. In addition, a plurality of flatpanel detectors different in visual field size (or radiographing area)are prepared, to permit use of a flat panel detector suited for ademanded visual field size, thereby providing a single apparatus whichcan be operated with plural visual field sizes.

FIGS. 8A and 8B show an example of a radiation imaging apparatus usingsuch a flat panel detector. FIG. 8A is a schematic diagram of astationary radiation imaging apparatus to be used with the apparatusfixed to the ceiling of a consulting room. FIG. 8B is a schematicdiagram of a mobile radiation imaging apparatus. In FIGS. 8A and 8B,reference numeral 801 denotes a radiation generating unit whichgenerates radiation such as X-rays; 802, a flat panel detector; and 803,a holding unit called a “C-type arm” for holding the radiationgenerating unit 801 and the flat panel detector 802. Reference numeral804 signifies a display unit capable of displaying radiation imageinformation derived by the flat panel detector 802; and 805, a bed forplacing thereon an object. In addition, reference numeral 806 indicatesa carriage which can carry the radiation generating unit 801, the flatpanel detector 802, the holding unit 803 and/or the display unit 804 andhas a structure capable of controlling them; and 807, a fitting unit forfitting the radiation generating unit 801, the flat panel detector, andthe holding unit 803.

DISCLOSURE OF THE INVENTION

As previously described, the radiation imaging apparatus using the flatpanel detector has advantages over a conventional radiation imagingapparatus using I.I.; however it does not always sufficiently meetrequirements in a medical site at present. In a medical site areperformed plain radiography such as X-raying to derive still images andfluoroscopic radiography to derive moving images for fluoroscopicdiagnosis. Since plain radiography aims to derive one image, it ispossible to derive an image using a large amount of radiation. On theother hand, fluoroscopic radiography needs to derive plural images, sothat the radiation dose per image used for capturing needs to besignificantly smaller than that used in plain radiography. For thisreason, a different operation control is required to make radiationimage information derived by a very small radiation dose almost equal inquality to an image signal derived by plain radiography. Furthermore, arequired radiographic area and radiation dose vary according to theradiographic properties different parts of the body, such as a head,chest and others. For this reason, an operation control varyingaccording to radiographically different parts of the body is required.Japanese Patent Application Laid-Open No. H11-009579 discloses theradiation imaging apparatus in which a plurality of flat panel detectorscorresponding to respective such radiographically different parts areprepared and detachably mounted. However, the preparation of a pluralityof flat panel detectors for each such type of radiography may increasethe cost of a radiation imaging apparatus and burden medicalinstitutions with a heavy cost. Furthermore, operation controls suitedfor respective flat panel detectors are required, which may complicatethe operation controls of the radiation imaging apparatus.

A radiation imaging apparatus of the present invention has a flat paneldetector which derives a radiation image based on incident radiation, aholding unit which holds the flat panel detector and a connectingmechanism capable of performing a connecting and a disconnecting betweenthe holding unit and the flat panel detector, where the connectingmechanism includes a mechanical connection unit which mechanicallyconnects the flat panel detector to the holding unit and a heattransmitting unit which transmits heat between the flat panel detectorand the holding unit.

Furthermore, a radiation imaging apparatus of the present inventionincludes a flat panel detector which derives a radiation image accordingto incident radiation, a holding unit which holds the flat paneldetector and a connecting mechanism capable of performing a connectingand disconnecting between the holding unit and the flat panel detector,where the flat panel detector can be controlled so that the maximumnumber of images derived by a continuous radiography that the flat paneldetector can perform in a state where the flat panel detector isdisengaged from the holding unit is smaller than the maximum number ofimages derived by the continuous radiography that the flat paneldetector can perform in a state where the flat panel detector is held bythe holding unit.

Furthermore, a radiation imaging apparatus of the present inventionincludes a holding unit which holds a flat panel detector which derivesa radiation image based on incident radiation, and a connectingmechanism capable of performing a connecting and a disconnecting betweenthe holding unit and the flat panel detector, where the connectingmechanism includes a mechanical connection unit which mechanicallyconnects the flat panel detector to the holding unit and a heattransmitting unit which transmits heat between the flat panel detectorand the holding unit.

The present invention enables performing plain radiography andshort-time fluoroscopic radiography with a flat panel detector removedfrom the holding unit and providing the radiation imaging apparatuscapable of handling various radiographic modes with portability, whichis a feature of the flat panel detector, maintained. In addition,various radiographic modes can be handled by a single flat paneldetector, which can suppress increase in cost of the radiation imagingapparatus and burden to medical institutions with cost.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-section of a flat panel detector and a holding unitillustrated with the flat panel detector fixed to the holding unit in aradiation imaging apparatus according to a first embodiment of thepresent invention.

FIG. 1B is a cross-section of the flat panel detector and the holdingunit illustrated with the flat panel detector removed from the holdingunit in the radiation imaging apparatus according to the firstembodiment of the present invention.

FIG. 2A is a cross-section of a flat panel detector and a holding unitillustrated with the flat panel detector fixed to the holding unit in aradiation imaging apparatus according to a second embodiment of thepresent invention.

FIG. 2B is a cross-section of the flat panel detector and the holdingunit illustrated with the flat panel detector removed from the holdingunit in the radiation imaging apparatus according to the secondembodiment of the present invention.

FIG. 3 is a cross-section of a flat panel detector and a holding unitillustrated with the flat panel detector fixed to the holding unit in aradiation imaging apparatus according to a third embodiment of thepresent invention.

FIG. 4A is a schematic perspective view illustrating the connectingmechanism of the flat panel detector.

FIG. 4B is a schematic perspective view illustrating the connectingmechanism of the holding unit.

FIGS. 5A, 5B and 5C are schematic perspective views illustrating amethod of connecting the flat panel detector to the holding unit in theradiation imaging apparatus according to the third embodiment of thepresent invention.

FIGS. 6A and 6B are schematic views illustrating an application of theradiation imaging apparatus of the present invention.

FIG. 7 is an equivalent circuit of the flat panel detector.

FIGS. 8A and 8B are schematic views illustrating a conventionalradiation imaging apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

The preferred mode for carrying out the invention is described belowwith reference to the drawings. Since the flat panel detector used inthe radiation imaging apparatus of the present invention can berepresented by the same equivalent circuit as in the conventional one,the flat panel detector is described by using FIG. 7.

In FIG. 7, reference numeral 701 denotes a converting unit; 702, aconverting element which converts radiation into electric charge; and703, a switching element which transfers the electric charge convertedby the converting element 702. The following two types are preferablyused for the converting elements 702: an indirect-converting typecomposed of a scintillator which converts radiation into light and aphotoelectric transducer which converts the converted light into anelectric charge; and a direct-converting type using a semiconductormaterial which directly converts radiation into an electric charge. ATFT composed of a thin film transistor or thin film diode is preferablyused as the switching element 703. In FIG. 7, a scintillator (not shown)and a MIS photoelectric transducer are used as the converting element702 and a TFT is used as the switching element 703. The presentinvention does not limit the converting element 702 to the MISphotoelectric transducer, but other photoelectric transducers such as,for example, a PIN photodiode or the like is applicable. A plurality ofconverting elements 702 of S11 to S33 are arranged. A plurality ofswitching elements 703 of T11 to T33 are also arranged. A pair of theconverting element 702 and the switching element 703, for example, apair of S11 and T11, forms one pixel. A plurality of such pixels arearrayed to form the converting unit 701. A driving wiring Vg1 iscommonly connected to the control electrodes of a plurality of theswitching elements T11 to T13 in a row direction. A driving wiring Vg2is commonly connected to the control electrodes of a plurality of theswitching elements T21 to T23 in a row direction. A driving wiring Vg3is commonly connected to the control electrodes of a plurality of theswitching elements T31 to T33 in a row direction. The driving wiringsVG1 to Vg3 are connected to a driving circuit 705 for driving andcontrolling the switching elements T11 to T33 for pixels. The drivingcircuit 705 provides the driving wirings Vg1 to Vg3 with driving signalsto allow a row-based driving control. In addition, a signal wiring Sig1is commonly connected to one of the source and the drain electrode of aplurality of the switching elements T11 to T31 in a column direction.Similarly, a signal wiring Sig2 is commonly connected to one of thesource and the drain electrode of a plurality of the switching elementsT12 to T32 in a column direction, and a signal wiring Sig3 is commonlyconnected to one of the source and the drain electrode of a plurality ofthe switching elements T13 to T33 in a column direction. The signalwirings Sig1 to Sig3 are connected to a signal processing circuit 706for reading analog signals based on electric charges converted by theconverting element 702 and transferred by the switching element. Thesignal processing circuit 706 includes an amplifying unit 707 composedof amplifiers AMP 1 to AMP 3 provided corresponding to the signalwirings Sig1 to Sig3 respectively. The signal processing circuit 706further includes sample hold units 708 composed of SH 1 to SH 3 whichtemporarily hold respective outputs of AMP 1 to AMP 3. The signalprocessing circuit 706 still further includes a multiplexer 709 whichconverts a parallel signal from the sample hold unit 708 (SH 1 to SH 3)into a series signal. Reference numeral 710 denotes an amplifierprovided at the rear stage of the signal processing circuit 706; and711, an A/D converter which converts an analog electric signal from thesignal processing circuit 706 into a digital signal. Reference numeral712 indicates a reference power supply unit for providing the signalprocessing circuit 706 with reference electric potential; and 704, apower supply unit for providing bias to a bias wiring Vs commonlyconnected to one electrode of respective converting elements S11 to S33.The other electrode of respective converting elements S11 to S33 isconnected to the other of the source and the drain electrode ofrespective switching elements T11 to T33.

In the next place, the operation of the flat panel detector is describedusing FIG. 7. First, the reference power supply unit 712 provides areference electric potential to the signal wiring to reset the signalwirings Sig1 to Sig3, and then the power supply unit 704 provides a biasto the converting elements S11 to S33 to enable them to perform theconverting operation. Next, radiation is caused to be incident on theconverting unit 701 with the switching elements T13 to T33 in thenonconducting state and the converting elements S11 to S33 convertradiation into an electric charge according to the incident radiation.The driving operation described below is conducted to read the convertedelectrical charges for each row from the converting unit 701. First, thedriving circuit 705 provides a driving signal to the driving wiring Vg1on a first row to bring the switching elements T11 to T13 connected tothe driving wiring Vg1 on the first row into conduction. The switchingelements T11 to T13 in the conducting state transfer the electricalcharges converted by converting elements S11 to S13 to the signalwirings Sig1 to Sig3 respectively. The transferred electric charges aretransmitted in parallel to the signal processing circuit 706, amplifiedby the amplifiers AMP 1 to AMP 3 connected to the signal wirings Sig1 toSig3 respectively and outputted in parallel as analog signals. Theoutputted analog signals are stored in parallel in the sample holdcircuits SH 1 to SH 3 provided at the rear stage of the amplifiers AMP 1to AMP 3. Parallel analog electrical signals from the sample holdcircuits SH 1 to SH 3 are converted into series signals by themultiplexer 709. The converted series signals are inputted into the A/Dconverter 711 through the amplifier 710 to perform an analog-to-digitalconversion, and outputted as one row of digital signal. After the analogelectric signals on the first-row have been outputted from theamplifiers AMP 1 to AMP 3 and stored in the sample hold circuits SH1 toSH 3, the signal wirings Sig1 to Sig3 are reset for the transfer of thefollowing row and then the electric charges on the second row aretransferred as is the case with those on the first row. Such a drivingoperation enables conversion to a series signal and conversion fromanalog to digital signal on the first row and transfer operation on thesecond row at the same period. Such a driving operation from the firstto the third row produces one image of radiation images or a plainradiation image. Repeating such a driving operation required for oneimage produces plural images of radiation images, and sequentiallyproducing plural images of radiation images produces fluoroscopicimages.

Thus, a medical site requires plural radiographic modes such as plainradiography and fluoroscopic radiography using a single radiationimaging apparatus with a flat panel detector. However, plain radiographyis different from fluoroscopic radiography in the required operationcontrol of a flat panel detector. The fluoroscopic radiography needs toproduce plural images of radiation images, so that the dose of radiationdelivered to an object to produce a single radiation image needs to besignificantly smaller than that used in plain radiography. The dose ofradiation delivered to an object to produce one radiation image influoroscopic radiography is 1 to 3 orders of magnitude lower than thatin plain radiography, although the exact ratio depends on the number ofradiation images to be used for fluoroscopic radiography. However, oneradiation image whether produced in plain radiography or in fluoroscopicradiography is required to be the same in quality, so that operationcontrol needs to be changed related in particular to the signalprocessing circuit of the flat panel detector. In other words, theamplification factor of the signal processing circuit in fluoroscopicradiography requires further increasing than that in plain radiography,or the sensitivity of the pixel requires increasing. For that reason,the signal processing circuit and the flat panel detector as a whole influoroscopic radiography consume more power than those in plainradiography, which leads to an increase in the heat quantity produced bythe signal processing circuit and the flat panel detector as a whole.Furthermore, fluoroscopic radiography typically takes more time thanplain radiography, which leads to an increase in consumption of power bythe signal processing circuit and the flat panel detector as a whole andin the resulting heat quantity produced, as well. As described earlier,the pixel used in the flat panel detector is composed of semiconductors,so that an increase in temperature causes dark current and leakagecurrent to increase, which may generate an artifact on radiation images.Furthermore, the signal processing circuit of the flat panel detector isalso composed of semiconductors, so that, again, a rise in temperatureincreases noise and causes variation in characteristics, which maygenerate an artifact on radiation images. When a radiation image is usedfor a medical diagnosis, those artifacts may result in degradation inpicture quality of the radiation image.

Consideration has been made to provide the flat panel detector with awater cooling mechanism which cools the detector by liquid using a heatpipe and an air cooling mechanism which cools the detector by air usinga fan in order to suppress rise in temperature of the flat paneldetector. However, it is important that the flat panel detector can becarried (hereinafter referred to as its “portability”). Providing theabovementioned cooling mechanism increases the weight of the flat paneldetector, degrading portability. In addition, if the flat panel detectorincreases in weight, it becomes difficult to attach the detector to ordetach the detector from the C-type arm used as the holding unit, and inaddition, the holding unit requires an increase in its mechanicalstrength.

In the present invention, the radiation imaging apparatus of which theflat panel detector is detachably mounted on the holding unit isconfigured as described in the following. When the maximum number ofimages derived by a radiography that the flat panel detector can performat a state that the flat panel detector is removed from the holding unitis “n”, and when the maximum number of images derived by the radiographythat the flat panel detector can perform at a state that the flat paneldetector is held by the holding unit is “m”, the flat panel detector isso controlled that m is greater than n (m>n). The flat panel detector isprovided with a heat radiator for radiating generated heat to theoutside. When continuous radiography is performed at a state that theflat panel detector is removed from the holding unit, the maximum numberof images of radiography that the flat panel detector can perform needsto be restricted. The reason is that the heat radiator requiressuppressing rise in temperature caused by heat in capturing to atemperature at which the flat panel detector is not adversely affected.That is to say, when the flat panel detector derives images in a statein which the flat panel detector is removed from the holding unit, it isimportant to restrict the number of images derived by the continuousradiography to a number equal to or smaller than the maximum number ofimages consistent with the heat radiator suppressing a rise intemperature to a prescribed temperature.

In a conversion unit 701 having pixels formed from a thin filmsemiconductor such as amorphous silicon, as the temperature rises, darkcurrent will increase. Due to the dark current, a noise componentcontained in the image signal increases. Thus, the S/N ratio will bedegraded. When the conversion unit 701 formed from a thin filmsemiconductor is maintained at a temperature equal to or lower than 50°C., a satisfactory S/N ratio required in a radiation imaging apparatuscan be secured. Accordingly, in a state in which the flat panel detectoris removed from the holding unit, it is desirable to set the maximumnumber n of the images so that the conversion unit 701 is maintained ata temperature equal to or lower than 50° C. In a signal processingcircuit 706 and A/D converter 711, as the temperature rises, powerconsumption and dark current increase. Thus, again, the S/N ratio willbe degraded. A temperature at which the signal processing circuit 706and the A/D converter 711 can operate normally is approximately equal toor lower than 70° C. Accordingly, in a state in which the flat paneldetector is removed from the holding unit, it is desirable to set themaximum number n of the images so that the signal processing circuit 706and the A/D converter 711 are maintained at a temperature equal to orlower than 70° C. It should also be noted that continuous radiographyinvolves radiographing with the flat panel detector without turning offa power source thereof, and includes plural times of still imageradiography and moving image fluoroscopy without turning off a powersource thereof.

On the other hand, the radiation imaging apparatus is equipped with acooling mechanism separately from the flat panel detector, and thecooling mechanism cools the flat panel detector through the holding unitwith the flat panel detector attached to the holding unit. The coolingmechanism may be provided in the holding unit or may be provided on acarriage or a fitting unit. In addition, the holding unit and/or theflat panel detector is provided with a connecting mechanism whichmechanically connects the flat panel detector. The connecting mechanismis provided with a mechanical connecting unit which performs amechanical connection with the flat panel detector, an electricconnecting unit which performs an electric connection with the flatpanel detector and a thermal connecting unit which thermally connectsthe heat radiator of the flat panel detector to the cooling mechanism totransfer the heat generated in the flat panel detector. Cooling heatgenerated in the flat panel detector by the cooling mechanism throughthe heat radiator and the thermal connecting unit enables the unit tocapture more radiation images with the flat panel detector attached tothe holding unit than can be done with the flat panel detector removedfrom the holding unit.

This allows performing plain radiography and short-time fluoroscopicradiography with the flat panel detector removed from the holding unitand providing the radiation imaging apparatus capable of handlingvarious radiographic modes with portability, which is a feature of theflat panel detector, maintained. In addition, various radiographic modescan be handled by a single flat panel detector, which avoids an increasein cost of the radiation imaging apparatus and burden to medicalinstitutions with cost.

The embodiments of the present invention are described in detail belowwith reference to the drawings.

First Embodiment

The first embodiment of the present invention is described in detailwith reference to FIGS. 1A and 1B. FIGS. 1A and 1B are enlargedcross-sections of a flat panel detector and a holding unit in theradiation imaging apparatus of the present invention. FIG. 1A is across-section illustrated with the flat panel detector fixed to theholding unit. FIG. 1B is a cross-section illustrated with the flat paneldetector removed from the holding unit.

In FIGS. 1A and 1B, reference numeral 101 denotes a scintillator; 102, afirst thermal diffusion plate; 103, a first heat pipe; 104, a signalprocessing circuit; 105, a cooling mechanism; 106, a C-type arm being aholding unit; 107, an electric wiring; 108, a second heat pipe; and 109,a second thermal diffusion plate. Reference numeral 110 indicates athermal conduction plate; 111, a connector being an electric connectingunit; 112, a fixing hook being a mechanical connecting unit; 113, ahousing; 114, a support base; 115, a sensor panel; 116, a circuit board;and 117, a cable.

The flat panel detector of the present embodiment is composed of thescintillator 101, the first thermal diffusion plate 102, the first heatpipe 103, the signal processing circuit 104, the connector 111, thehousing 113, the support base 114, the sensor panel 115 and the circuitboard 116. The sensor panel 115 has such a structure that a plurality ofpixels including photoelectric transducers and TFTs are arranged in twodimensions on an insulating substrate such as glass, and drivingwirings, signal wirings and bias wirings are provided. The sensor panel115 has a configuration illustrated in the equivalent circuit in brokenline in FIG. 7. The scintillator 101 is arranged on the incoming side ofradiation on the sensor panel 115 and converts the incident radiationinto light in a wavelength range which the photoelectric transducers inthe sensor panel 115 can detect. In the present embodiment, theconverting element 702 in FIG. 7 is composed of the photoelectrictransducer and the scintillator corresponding thereto. The signalprocessing circuit 104 reads a radiation image signal from the sensorpanel 115 and is a semiconductor circuit composed of the amplifier 707,the sample hold unit 708 and multiplexer 709 in FIG. 7. The circuitboard 116 has an integrated circuit with the amplifier 710 and the A/Dconverter 711 in FIG. 7, a signal processing circuit which processes theread signal, a control circuit which controls a driving circuit (notshown) and the signal processing circuit 104 and a power supply circuit.The connector 111 electrically connects the flat panel detector to theelectric wiring 107 provided on the C-type arm 106. The first heat pipe103 conducts heat generated in the signal processing circuit 104 to thefirst thermal diffusion plate 102 and is disposed in contact with thefirst thermal diffusion plate 102. The term heat pipe is a generic termfor a heat conduction system utilizing phase change such asvaporization/liquefaction of liquid sealed inside and capillarity. Theheat pipe is very high in heat conductivity and efficiently conductsheat. The heat pipe has a higher degree of freedom in shape, has nomovable part and is maintenance-free, which is suited for apparatusrequiring high reliability such as medical equipment. The thermaldiffusion plate 102 is a member for radiating heat conducted from thefirst heat pipe 103 to the outside of the flat panel detector. In FIG.1A, the thermal diffusion plate 102 conducts heat in contact with thethermal conduction plate 110 provided on the C-type arm 106. As show inFIG. 1B, the first thermal diffusion plate 102 radiates heat generatedin the flat panel detector outside by natural heat radiation with theflat panel detector removed from the C-type arm. In other words, in thepresent embodiment, the first heat pipe 103 and the first thermaldiffusion plate 102 form a heat radiator. It is preferable to use metalhigh in heat conductivity such as copper or aluminum as a material ofthe first thermal diffusion plate 102. The support base 114 supports thesensor panel 115, circuit board 116 and the signal processing circuit.The housing 113 is a container which holds the scintillator 101, thefirst thermal diffusion plate 102, the first heat pipe 103, the signalprocessing circuit 104, the connector 111, the support base 114, thesensor panel 115 and the circuit board 116 in its inside.

On the other hand, the C-type arm 106 is composed of the coolingmechanism 105, the electric wiring 107, the second heat pipe 108, thesecond thermal diffusion plate 109, the thermal conduction plate 110,the connector 111 and the fixing hook 112. The thermal conduction plate110 serves to conduct heat conducted from the first thermal diffusionplate 102 of the flat panel detector to the second thermal diffusionplate 109 provided on the C-type arm 106. It is preferable to use asheet material using silicone rubber or acrylic rubber high in heatconductivity as a material for the thermal conduction plate 110.Connecting the metallic thermal diffusion plates with each otherprecludes heat from being efficiently conducted because of air spaceproduced between the plates, which can be prevented by the above sheetmaterial. The second thermal diffusion plate 109 conducts heat conductedthrough the thermal conduction plate 110 to the second heat pipe 108. Itis preferable that the second thermal diffusion plate 109 uses the samematerial as the first thermal diffusion plate 102. The second heat pipe108 conducts heat conducted from the second thermal diffusion plate 109to the cooling mechanism 105 for cooling it. It is preferable that thesecond heat pipe 108 uses the same material as the first heat pipe 103.The cooling mechanism 105 cools heat conducted by the second heat pipe108. In the present embodiment, the second heat pipe 108, the secondthermal diffusion plate 109 and the thermal conduction plate 110 form athermal connecting unit. The electric wiring 107 supplies the flat paneldetector with a power source and an electric signal required to drive itthrough the connector 111 from the C-type arm 106 and transmits aradiation image signal from the flat panel detector and a system-statussignal to the C-type arm 106. The fixing hook 112 mechanically holds theflat panel detector in the C-type arm and functions as a mechanicalconnecting unit. On the sides of the housing 113 of the flat paneldetector are formed grooves which are caught on the fixing hook 112 tofix the flat panel detector to the C-type arm.

In the present embodiment, the first heat pipe 103 and the first thermaldiffusion plate 102, which are a heat radiator, conduct heat generatedin the signal processing circuit 104 of the flat panel detector to thecooling mechanism 105 through the thermal conduction plate 110, thesecond thermal diffusion plate 109 and the second heat pipe 108, whichare a thermal connecting unit, for cooling it with the flat paneldetector fixed to the C-type arm. In addition, the first thermaldiffusion plate 102 radiates heat generated in the flat panel detectoroutside by natural heat radiation with the flat panel detector removedfrom the C-type arm. Thus, capturing images with the flat panel detectorfixed to the C-type arm 106 enables capturing more radiation images thanthat with the flat panel detector removed from the C-type arm 106.

In the present embodiment, a cable extension 117 is used for electricalconnection when the flat panel detector is removed from the C-type arm106. However, the present invention is not limited to the cableextension, but a known radio communication may be used to transmit andreceive radiation image data, and the flat panel detector may beprovided with a separate power supply.

Second Embodiment

The second embodiment of the present invention is described in detailwith reference to FIGS. 2A and 2B. FIGS. 2A and 2B are enlargedcross-sections of a flat panel detector and a holding unit in theradiation imaging apparatus of the present invention. FIG. 2A is a crosssection illustrated with the flat panel detector fixed to the holdingunit. FIG. 2B is a cross-section illustrated with the flat paneldetector removed from the holding unit. Incidentally, the same referencenumerals are used for the same composing elements as in the firstembodiment to omit the detailed descriptions thereof.

Reference numeral 201 represents a connector electrically connecting theflat panel detector to the electric wiring 107 provided on the C-typearm 106. Reference numeral 202 denotes a fitting of metal such as copperhigh in heat conductivity which is so configured as to bring a firstheat pipe 203 into contact with a second heat pipe 204 to conduct heatfrom the first heat pipe 203 to the second heat pipe 204. Referencenumeral 203 designates a first heat pipe to conduct heat generated inthe signal processing circuit 104 to the fitting 202. Reference numeral204 represents a second heat pipe to conduct heat conducted from thefirst heat pipe 203 through the fitting 202 to the cooling mechanism 105to cool it. Reference numeral 205 denotes an electric connecting unit ofthe flat panel detector.

In the present embodiment, the fitting 202 conducts heat between thefirst heat pipe 203 and the second heat pipe 204 instead of the firstthermal diffusion plate 102, the thermal conduction plate 110 and thesecond thermal diffusion plate 109. In the present embodiment, the firstheat pipe 203 is provided as a heat radiator, and the fitting 202 andthe second heat pipe 204 are provided as a thermal connecting unit.

In the present embodiment, a heating portion is not exposed to thesurface of the housing 113 of the flat panel detector, so that theheating portion is not exposed when the flat panel detector is removedfrom the C-type arm 106, which enhances safety, in addition to the sameeffect as in the first embodiment. The apparatus in the presentembodiment further decreases in weight by the amount corresponding tothe weight of the thermal diffusion plate than that in the firstembodiment, which improves portability.

Third Embodiment

The third embodiment of the present invention is described in detailwith reference to FIGS. 3 to 5C. FIG. 3 is a cross section illustratedwith the flat panel detector fixed to the holding unit. FIG. 4A is aschematic perspective view illustrating the connecting mechanism of theflat panel detector and FIG. 4B is a schematic perspective viewillustrating the connecting mechanism of the holding unit. FIGS. 5A, 5Band 5C are schematic perspective views illustrating a method ofconnecting the flat panel detector to the holding unit. Incidentally,the same reference numerals are used for the same composing elements asin the first or the second embodiment to omit the detailed descriptionsthereof.

In the present embodiment, mechanical, electric and thermal connectionsare made using a first connecting mechanism provided on the flat paneldetector and a second connecting mechanism provided on the C-type arm106 that serves as a holding unit. Reference numeral 301 denotes a flatpanel detector of the present embodiment and includes the scintillator101, the first heat pipe 103, the signal processing circuit 104, thehousing 113, the support base 114, the sensor panel 115, the circuitboard 116, a first connecting mechanism 302 and a connector 307.Reference numeral 302 signifies a first connecting mechanism to radiateheat conducted from the first heat pipe 103 to the outside of the flatpanel detector 301 and to make connection of the flat panel detector 301to the second connecting mechanism of the C-type arm 106 to conductheat. The first connecting mechanism 302 has a heat radiating member 302a for radiating heat outside or conducting heat to the second connectingunit and a fixing member 302 b for mechanically connecting the flatpanel detector 301 to the second connecting mechanism of the C-type arm106. A flange including a metallic part high in heat conductivity ispreferably used for the first connecting mechanism 302. Referencenumeral 303 denotes a heat conducting member to conduct heat from theheat radiating member 302 a to the cooling mechanism 105 through thesecond heat pipe 108. A flange including a metallic part high in heatconductivity is preferably used for the heat conducting member 303 as isthe case with the heat radiating member 302 a. Reference numeral 304represents a fixing member for fixing the first connecting mechanism302, for example, by inserting a pin into a notch provided in the firstconnecting mechanism 302 or by forcibly pressing the first connectingmechanism 302 downward. Reference numeral 305 indicates a bearing torotatably support a wiring connecting unit 306. Reference numeral 306indicates a wiring connecting unit which is cylindrical and includes anelectric wiring 107 therein. Reference numeral 307 denotes a connectorof the flat panel detector 301 which makes electrical connection withthe electric wiring 107. In the present embodiment, the secondconnecting mechanism of the C-type arm 106 includes the heat conductingmember 303, the fixing member 304, the bearing 305 and the wiringconnecting unit 306. The heat conducting member 303 and the second heatpipe 108 form a thermal connecting unit.

In the next place, a method of fixing the flat panel detector 301 to theC-type arm 106 of the present invention is described using FIGS. 5A to5C. First, as shown in FIG. 5A, the protrusions provided on the firstconnecting mechanism 302 of the flat panel detector 301 are mated withnotches provided on the heat conducting member 303 of the C-type arm106. As shown in FIG. 5B, the flat panel detector 301 is pressed intothe C-type arm 106 with the protrusions mated with the notches. At thispoint, the fixing member 302 b is positioned inside the heat conductingmember 303. Furthermore, the wiring connecting unit 306 of the C-typearm 106 is connected to the connector 307 of the flat panel detector 301to establish an electrical connection. As shown in FIG. 5C, with theflat panel detector 301 pressed into the C-type arm 106, the flat paneldetector 301 is rotated by a predetermined angle to complete fixing.

(Application)

FIGS. 6A and 6B illustrate an application of a mobile radiation imagingapparatus using the present invention. FIG. 6A is an example showing acase where radiography is conducted using a radiation source 401provided on the C-type arm with the flat panel detector removed from theC-type arm, in a mobile radiation imaging apparatus capable ofperforming fluoroscopic radiography and still image photography. Here,reference numeral 401 denotes a radiation generating unit; 405, a flatpanel detector; 404, a C-type arm for holding the radiation generatingunit 401 and the flat panel detector 405. Reference numeral 403represents a display unit capable of displaying radiation imageinformation derived by the flat panel detector 405; and 406, a bed forplacing thereon an object 408. Reference numeral 409 denotes a carriagecapable of carrying the radiation generating unit 401, the flat paneldetector 405 and the C-type arm 404; and 402, a mobile system capable ofcontrolling those. In this application, the flat panel detector 405 iscapable of deriving images within the maximum number of images ofradiation images “n” consistent with the heat radiator described in theabove embodiment suppressing a rise in temperature to a temperature atwhich the flat panel detector is not adversely affected, for example,the flat panel detector 405 can perform a still image photography and ashort-time fluoroscopic radiography. In addition, with the flat paneldetector 405 fixed to the C-type arm 404, heat generated in the flatpanel detector 405 is cooled by the cooling mechanism through the heatradiator and the thermal connecting unit shown in the foregoingembodiment. Thus, having the flat panel detector 405 fixed to the C-typearm 404 enables capturing more radiation images than is possible withthe flat panel detector 405 removed from the C-type arm 404.

FIG. 6B is an example showing a case where radiography is conductedusing another radiation generating unit 407 instead of radiationgenerating unit 401 provided on the C-type arm 404 with the flat paneldetector 405 removed from the C-type arm 404, in a mobile radiationimaging apparatus capable of performing fluoroscopic radiography andstill image photography. Reference numeral 407 denotes a radiationgenerating unit mounted in advance. In this application as well, as isthe case with the above embodiment, the flat panel detector 405 iscapable of deriving images within the maximum number of images ofradiation images “n” that is consistent with the heat radiatorsuppressing a rise in temperature to a temperature at which the flatpanel detector is not adversely affected, for example, the flat paneldetector 405 can perform a still image photography and a short-timefluoroscopic radiography. In addition, with the flat panel detector 405fixed to the C-type arm 404, heat generated in the flat panel detector405 is cooled by the cooling mechanism through the heat radiator and thethermal connecting unit stated in the foregoing embodiment. Thus, havingflat panel detector 405 fixed to the C-type arm 404 enables capturingmore radiation images than is possible with the flat panel detector 405removed from the C-type arm 404.

The present invention relates to a radiation imaging apparatus suitedfor use in medical diagnosis, and in particular, to a radiation imagingapparatus including a flat panel detector composed of a semiconductorelement as a detector.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

1. A radiation imaging apparatus comprising: a flat panel detector forderiving a radiation image based on incident radiation; a holding unitwhich holds the flat panel detector; and a connecting mechanism capableof performing a connecting and a disconnecting between the holding unitand the flat panel detector, wherein the connecting mechanism includes amechanical connection unit which mechanically connects the flat paneldetector to the holding unit and a heat transmitting unit whichtransmits heat between the flat panel detector and the holding unit, theheat transmitting unit comprising a heat pipe.
 2. The radiation imagingapparatus according to claim 1, wherein the connecting mechanismincludes further an electric connection unit which electrically connectsthe flat panel detector to the holding unit.
 3. The radiation imagingapparatus according to claim 1, wherein the flat panel detector isprovided with a converting unit having a substrate, and having on thesubstrate a plurality of pixels which act as a converting unit thatconverts the radiation into an electric signal and transfers theelectric signal and a signal processing circuit for processing theelectric signal read out from the converting unit.
 4. The radiationimaging apparatus according to claim 3, wherein each of the pixelsincludes a converting element which converts the radiation into anelectric signal and a switching element which transfers the electricsignal.
 5. The radiation imaging apparatus according to claim 4, whereineach of the converting elements includes a scintillator which convertsthe radiation into light and a photoelectric transducer which convertsthe light into the electric signal.
 6. The radiation imaging apparatusaccording to claim 1, further comprising a radiation generatingapparatus held with the holding unit.
 7. A radiation imaging apparatuscomprising: a holding unit which holds a flat panel detector forderiving a radiation image based on incident radiation; and a connectingmechanism capable of performing a connecting and a disconnecting betweenthe holding unit and the flat panel detector, wherein the connectingmechanism includes a mechanical connection unit which mechanicallyconnects the flat panel detector to the holding unit and a heattransmitting unit which transmits heat between the flat panel detectorand the holding unit, the heat transmitting unit comprising a heat pipe.8. The radiation imaging apparatus according to claim 7, wherein theconnecting mechanism includes further an electric connection unit whichelectrically connects the flat panel detector to the holding unit.